Filament support for tubular incandescent lamps



M 23, 1963 H. B. KIMBALL 3,385,993

FILAME TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT PS Filed Aug. 16, 1965 INVENTOR Afiw' Henry B. Kimball United States Patent 01 ice 3,385,993 Patented May 28, 1968 3,385,993 FILAMENT SUPPORT FOR TUBULAR INCANDESCENT LAMPS Henry B. Kimball, Mountain Lnlres, N151, assignor to Westinghouse Electric Corporation, Pittsburgh, Pa.,

a corporation of Pennsylvania Filed Aug. 16, 1965, Ser. No. 479,998 7 Claims. (Cl. 313-271) The present invention rel-ates to incandescent electric lamps and, more particularly, to a filament support for a tubular incandescent lamp wherein the filament extends for substantially the entire length of such lamp.

Heretofore it has been customary to utilize one or more auxiliary supports along the length of the lamp which engages both the wall of the tubular envelope and the elongated filament for the purpose of supporting the latter substantially on the envelope axis. Such supports have usually taken the form of wire loops or spirals and also metallic disks that are separately formed and attached to the filament. In either case, the proper application of such supports to the elongated refractory metal filament has been a tedious and critical operation which increased the manufacturing costs of the larnp.

It is accordingly the primary object of the present invention to provide a tubular electric lamp having an elongated filament and wherein such filament is provided with an integral support engage-able with the interior wall of the lamp envelope for supporting the filament in a desired position within the lamp.

Another object of the present invention is the provision of a tubular electric lamp having an elongated filament and wherein the latter is provided with an integral support formed at the time of coiling such filament which engages the wall of the tubular envelope and maintains the filament in a desired location within the lamp.

A further object is the provision of an elongated refractory metal filament for a tubular incandescent lamp wherein such filament is provided with a turn of increased diameter sufficient to contact the inner surface of the tubular envelope and maintain the elongated filament substantially on the axis of the envelope.

Still another object is the provision of a method for manufacturing such a filament.

The foregoing objects of the present invention, together with other objects which will become apparent to those skilled in the art from the following description, are achieved by providing a coiled elongated refractory metal filament wherein such filament is provided with one or more spaced convolutions or turns of enlarged diameter. The diameter of these turns approximate that of the interior of the tubular envelope of the lamp so as to bear on the surface thereof when the elongated coiled filament is inserted into the envelope during fabrication of the lamp, thus holding the filament in a desired position substantially on the axis of the finished lamp.

The present invention can be readily understood by reference to the accompanying drawing, wherein:

FIGURE 1 is a perspective view of an elongated refractory metal filament for an electric lamp constructed in accordance with the present invention;

FIGURE 2 is a view identical to that of FIG. 1 except that it illustrates a plurality of spaced enlarged-diameter turns for supporting the elongated coiled filament interiorly of a tubular envelope;

FIGURE 3 is a perspective view similar to that shown in FIG. 1 except that the enlarged support turns are twisted during formation to electrically short-circuit them;

FIGURE 4 is a schematic view showing the mandrel Wire in the chucks of the coiling machine head together with the transversely movable idler pulleys at the beginning of the coil-winding operation;

FIGURE 5 is a view similar to FIG. 4 but showing completion of the coil-winding operation with the elongated coiled filament wound on the mandrel together with spaced enlarged loops twisted upon themselves adjacent their juncture with the coiled filament body;

FIGURE 6 is a sectional view through the elongated coiled filament on the mandrel along the line Vl-VI; and

FIGURE 7 is an end view of the completed elongated coiled filament with its twisted enlarged-diameter support turns, as shown in FIG. 3.

Referring now more specifically to the drawing, in FIG. 1 there is shown an elongated coiled filament 10 of refractory metal wire, such as tungsten, that is provided with a reverse bend or retroverted turn 11 of enlarged diameter. This expanded turn 11 has a diameter of such size that it will contact the inner surface of the tubular lam-p envelope in which it is to be sealed and thus support the coiled filament 10 in proper position therein, preferably on the longitudinal axis of the finished lamp.

The modification shown in FIG. 2 is identical to that of FIG. 1 except that the coiled filament 10a in such modification is longer and is thus adapted for use in an elongated quartz iodine-filled lamp or the like, and in addition, several spaced retroverted enlarged-diameter support turns are provided, with the total number thereof depending upon the overall length of the elongated coiled filament.

The difficulty with the construction shown in FIGS. 1 and 2 resides in the fact that the enlarged retroverted support turns 11 and 11a are an integral part of the electrical circuit and, hence, are heated to an exceedingly high temperature along with the rest of the filament turns when the lamp is energized. Since these support turns are in contact with the inner surface of the tubular envelope, the high operating temperature of such turns causes dev-itrification of the quartz envelope in a relatively short period of time, thus materially reducing the useful life of the lamp.

The aforesaid difficulty is completely eliminated by the modification of the present invention shown in FIGS. 3 and 7, wherein the retroverted large-diameter support turn 11b is twisted at a location 12 adjacent the periphery of the main coiled filament 1%. These several twists 12 electrically short circuit the coil turn that forms the support 11b so that no current flows through the latter. Hence, the support turn is not heated as is the remainder of the elongated coiled filament 10b. When such filament is subsequently mounted in a completed lamp, the support turn 11b is accordingly not electrically heated over the area which contacts the Wall of the elongated tubular envelope thus eliminating the devitrification problem.

The method and apparatus for winding an elongated filament coil 19b with a plurality of twisted retroverted turns forming spaced arcuate support-s lllb are shown in FIGS. 4, 5 and 6. The refractory metal wire 14 is threaded over spring-loaded hooks 16 and clamped to the mandrel 17 by the chucks 18 and 19 which also hold and rotate the mandrel. Each of these hooks 16 is secured by an elongated spring 20 to an open hoop or ring 22, only one of which is shown in FIG. 4. Such ring 22 is held con-centric with the mandrel 17 by three rollers 24 spaced approximately apart and bearing on the outer periphery of each ring 22. At least one of these rollers 24 for each ring 22 is affixed to a drive shaft 26 so that such driven roller 24 causes rotation of each ring 22 and its hooks 16 about the mandrel 17 as its axis through a circular path around the mandrel.

It is to be noted, however, that alternate rings 22 are rotated by their respective drive shafts 26 and driven rollers 24 in opposite directions so that the refractory metal wire 14- passing through the books 16 is likewise wound in opposite directions on the mandrel 17 for a distance corresponding to the horizontal spacing between such hooks 16. For example, assuming the four rings 22 at a given instant during their rotation position their respective hooks 16 so that two are disposed below the mandrel 17 and two thereabove, as illustrated in FIG. 4, then both rings 22 having their hook-s 16 above the mandrel 17 will be rotated in the same direction by the drive shaft 26 and their respective drive rollers 24. At the same time the rings 22 together with their respective hooks 16 which are disposed below the mandrel 17 will be rotated together by their drive shaft (not shown) in the opposite direction.

The rotation of the mandrel 17 by the chucks 18 and 19 with attendant coiling of the refractory metal wire 14 tightly about such mandrel will exert a substantial pull on the respective hooks 16. As this increases with continued coiling, the elongated springs 20 supporting each hook 116 are caused to expand until the elongated filamentary coil 16b is formed, as shown in FIGS. 5 and 6, at which time the hooks 16 will have approached their closest point to the mandrel 17 and rotation of the latter together with the rings 22 are then stopped. The hooks 16 are then given a couple of turns about the axis of their supporting springs 20 to form the twists 12 (FIGS. 3 and 7) after which the hooks 16 are removed from the remaining wire loops 28.

Such loops are then closed and bent to form the arcuate large-diameter support turns 11b, and the mandrel 17 is withdrawn to t-hus complete the elongated coiled filament 10b, as shown in FIGS. 3 and 7, which filament has a plurality of spaced enlarged supporting turns 11b. It should be apparent that, if desired, the formation of the twist 12 can be made at the time of intially threading the refractory metal wire 14 over the hooks 16 before commencement of the coiling by the mandrel 17. Also, instead of the open loops 28 as shown in FIG. 5 resulting upon completion of the coiling of the wire 14 on the mandrel 17, such loops 28 can be closed as shown by the retroverted loops in FIGS. 1, 2 and 3 by proper shaping of the hooks 16 themselves to produce such closed loops, again, prior to commencement of the coiling operation.

The finished filament 1017 thus comprises a plurality of coiled segments that are joined by spaced retroverted turns 11b of enlarged diameter, wherein the turns comprising said segments are of substantially uniform diameter and wound in opposite directions.

It should thus be apparent to those skilled in the art that an elongated coiled refractory wire filament together with the method of producing it has been herein shown and described in which such elongated filament is provided with one or more integral supporting members or turns of expanded or enlarged diameter. Such supporting turns are formed from reverse bend loops of the filament wire itself and extend around the adjacent body portions of the elongated coiled filament. These support turns are dimensioned to engage the inner surface of the tubular envelope and thus maintain the filament substantially on the longitudinal axis of the completed electric lamp. Moreover, in a preferred filament embodiment the retroverted supporting turns are each provided with a twist adjacent the juncture of the turn with the coiled body portion of the filament thereby short-circuiting the turns. Passage of the filament current through the support turns and the ensuing heating thereof and devitrification of the quartz envelope of the finished electric lamp are thereby prevented.

Although several modifications of the present invention have been herein shown and described, it is to be tinderstood that still further modifications thereof may be made without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. An elongated goiled filament for an incandescent llamp having a tubular envelope, which filament comprises:

(a) a plurality of spaced turns of refractory metal wire that are of substantially uniform diameter and comprise the body portion of said filament, and

(b) a retroverted turn that is formed from said wire and is located intermediate the ends of the coiled filament, said retroverted turn having a diameter larger than the turns comprising said body portion and thereby constituting an integral arcuate support that is adapted to engage the inner surface of the tubular envelope when said filament is inserted into said envelope.

2. The elongated coiled filament set forth in claim 1 wherein; said retroverted turn divides the filament into two coiled segments, and the turns comprising said segments are wound in opposite directions.

3. An elongated coiled filament for an incandescent lamp having a tubular envelope, which filament comprises:

(a) a plurality of closely spaced turns of refractory metal wire that are of substantially uniform diameter and comprise the body portion of said filament, and

(b) a plurality of spaced retroverted turns that are formed from said wire and divide the filament into a plurality of coiled segments at preselected points along its length, said retroverted turns having a di ameter larger than the turns comprising said body portion and being of such dimension that they constitute integral arcuate supports that are adapted to engage the inner surface of the tubular envelope and maintain the coiled filament substantially on the axis of said envelope when said filament is inserted there- 4. A coiled filament of refractory metal for a tubular electric lamp comprising:

(a) a plurality of spaced turns of refractory metal wire of substantially the same diameter,

(b) a retroverted turn formed in said filament between the ends thereof and having a larger diameter approximating that of the tubular envelope of said electric lamp for engaging the interior wall of the latter to form a support for naintaining said coiled filament substantially on the axis of said tubular envelope when inserted therein, and

(c) a short-circuiting twist in said retroverted turn adjacent the juncture thereof with the closely spaced turns of said coiled filament to prevent the flow of electrical energy through said retroverted turn and thereby eliminate heating thereof with ensuing devitrification of said tubular envelope at its contact area with saio retroverted supporting turn.

5. An elongated coiled filament of refractory metal for a tubular electric lamp comprising:

(a) a plurality of closely spaced turns of refractory metal wire of substantially the same diameter along the axis of said coiled filament,

(b) a plurality of spaced retroverted turns formed from said refractory metal wire intermediate the ends of said coiled filament and having a larger diameter approximating that of the tubular envelope of said electric lamp for engaging the interior wall of the latter to form spaced supports for maintaining said coiled filament substantially on the axis of said tubular envelope when inserted therein, and

(c) a short-circuiting twist in each of said retroverted turns adjacent the juncture thereof with the respective closely spaced turns of said coiled filament to prevent the How of electrical energy through said retroverted turns and thereby eliminate heating thereof with ensuing devitrifieation of said tubular envelope at its contact area with each said retroverted supporting turn.

6. The method of making an elongated coiled filament for a tubular electric lamp, wherein said filament is provided with a retroverted turn of enlarged diameter that serves as an arcuate support for said filament when the latter is inserted into the lamp envelope, which method comprises:

(a) Winding preselected portions of a refractory metal wire upon a mandrel to form a pair of coil segments that are joined by an uncoiled section of wire and have turns of substantially uniform diameter,

(b) forming said uncoiled wire section into a retroverted turn of enlarged diameter that is concentric with the turns of said coil segments, and then (c) removing the mandrel from the resulting coiled filament.

7. The method of making an elongated coiled filament for a tubular electric lamp, wherein said filament is provided with spaced retroverted turns of enlarged diameter that serve as arcuate supports for said filament when the latter is inserted into the lamp envelope, which method comprises:

(a) winding a refractory metal wire to form a plurality of spaced coil segments of substantially the same diameter that are joined by uncoiled wire segments,

(b) forming said uncoiied wire segments into retroverted turns of enlarged diameter that extend beyond the body of said filament, and then (c) twisting each of the retroverted turns adjacent the juncture thereof with the closely spaced turns of said coil segments to prevent the flow of electrical energy through said retroverted turns when the filament is subsequently incorporated into an electric lamp and energized.

References Cited UNITED STATES PATENTS 1,125,121 1/1915 Knight 313-278 X 1,125,744 1/1915 Scott 313--278 X 3,194,999 7/1965 Heinlein 313271 3,211,941 10/1965 Sanden et a1 313274 X 3,223,875 12/1965 Eggers 3l3--271 X JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner. 

1. AN ELONGATED COILED FILAMENT FOR AN INCANDESCENT LAMP HAVING A TUBULAR ENVELOPE, WHICH FILAMENT COMPRISES: (A) A PLURALITY OF SPACED TURNS OF REFRACTORY METAL WIRE THAT ARE OF SUBSTANTIALLY UNIFORM DIAMETER AND COMPRISE THE BODY PORTION OF SAID FILAMENT, AND (B) A RETROVERTED TURN THAT IS FORMED FROM SAID WIRE AND IS LOCATED INTERMEDIATE THE ENDS OF THE COILED FILAMENT, SAID RETROVERTED TURN HAVING A DIAMETER LARGER THAN THE TURNS COMPRISING SAID BODY PORTION AND THEREBY CONSTITUTING AN INTEGRAL ARCUATE SUPPORT THAT IS ADAPTED TO ENGAGE THE INNER SURFACE OF THE TUBULAR ENVELOPE WHEN SAID FILAMENT IS INSERTED INTO SAID ENVELOPE. 